On the association between northward turnings of the interplanetary magnetic field and substorm onsets

We re-examine whether substorms are triggered by solar wind fluctuations or an internal magnetospheric instability by comparing the statistical associations between substorm onsets and (1) an external trigger definition, (2) a simple internal trigger definition of only prior loading of solar wind energy that is a subset of the external trigger definition. Statistical associations are calculated both for observed substorm onsets and onsets generated by a Minimal Substorm Model in which substorms are purely internally triggered. Thence we argue that a minimum interval of prior loading is a necessary condition for substorm onset, a subsequent northward IMF turning is not necessary, and consequently that an internal trigger from a magnetospheric instability is a necessary and sufficient condition for substorm onset. We discuss how this result may explain a report that externally triggered substorms are systematically larger than non-externally triggered substorms.

Details

Publication status:
Published
Author(s):
Authors: Morley, S.K., Freeman, M.P. ORCIDORCID record for M.P. Freeman

On this site: Mervyn Freeman
Date:
1 January, 2007
Journal/Source:
Geophysical Research Letters / 34
Page(s):
6pp
Digital Object Identifier (DOI):
https://doi.org/10.1029/2006GL028891